1. Field of the Invention
This invention relates to an image printing method and device for printing a print image on a printing object by using an ink.
2. Prior Art
Conventionally, the method of printing a print image by using an ink includes a dot impact method and a thermal method which use a ribbon containing ink or the like, as well as an ink jet printing method in which ink droplets are ejected. In the ink jet printing method, for instance, printing is carried out by blowing (ejecting) ink droplets corresponding to dots of a desired print image onto a printing object from nozzles of an ink jet head (print head). When the print image is a color image, inks of three primary colors of C (cyan), M (magenta), and Y (yellow), or four basic colors of the three primary colors plus K (black) are ejected to corresponding dots of a print image according to a desired print color of the print image, to thereby carry out color printing.
The image printing method of the above-described kind which uses inks, particularly, the ink jet printing method, suffers from a problem of degradation of quality of a printed image due to mixing of adjacent printed dots through blotting of ink on the printing object or on the contrary due to increased space between printed dots caused by limited spreading of ink on the printing object. That is, even if ink is ejected to the center of each print dot, the size and density of the printed dot varies with the degree of permeation of ink into the printing object (hereinafter referred to as xe2x80x9cpenetration ratexe2x80x9d), which can prevent a print image having a desired quality from being obtained even if printing control conditions, such as a print density (reciprocal of a distance between centers of adjacent print dots), are set to predetermined suitable conditions.
It is an object of the invention to provide an image printing method and device which is capable of maintaining quality of a print image printed on a printing object by using ink even when the penetration rate of ink into the printing object has changed.
To attain the above object, according to a first aspect of the invention, there is provided a method of printing a print image on a printing object by using ink, comprising the steps of:
detecting factors causing a change in a penetration rate of at least one kind of ink into the printing object;
setting printing control conditions in dependence on results of detection of the factors causing the change in the penetration rate; and
printing the print image on the printing object by using the at least one kind of ink based on print image data representative of the print image and the printing control conditions.
To attain the above object, according to a second aspect of the invention, there is provided an image printing device comprising:
a penetration rate-changing factor-detecting section for detecting factors causing a change in a penetration rate of at least one kind of ink into a printing object;
a printing control condition-setting section for setting printing control conditions in dependence on results of detection of the factors causing the change in the penetration rate; and
an image printing section for printing the print image on the printing object by using the at least one kind of ink based on print image data representative of the print image and the printing control conditions.
According to the image printing method and device, factors causing a change in a penetration rate of at least one kind of ink into a printing object are detected, and printing control conditions are set in dependence on results of detection of the factors causing the change in the penetration rate. The print image is printed on the printing object by using the at least one kind of ink based on print image data representative of the print image and the printing control conditions. That is, by detecting the factors causing the change in the penetration rate of ink, a change of the penetration can be expected, and the printing control conditions are set according to the results of detection of the factors causing the change. Therefore, it is possible to set suitable printing control conditions according to the change in the penetration rate, and the print image is printed based on the printing control conditions thus set. Therefore, even if the penetration rate of the ink into the printing object has changed, it is possible to maintain the quality of a print image printed on the printing object by using the ink.
Preferably, the printing control conditions include a print density which is inversely proportional to a distance between centers of adjacent print dots of the print image.
As described hereinbefore, if the penetration rate of the ink into the printing object has changed, the quality of the print image can be degraded due to mixing of adjacent printed dots or on the contrary due to increased space between printed dots caused by limited spreading of ink on the printing object. According to the preferred embodiment of each aspect of the invention, the printing control conditions based on which printing is controlled include a print density which is inversely proportional to a distance between centers of adjacent print dots of the print image, and hence it is possible to set the print density according to the change in the penetration rate of ink into the printing object, whereby even if the penetration rate of ink into the printing object has changed, the quality of a print image printed by using the ink can be maintained.
Preferably, the step of printing the print image includes printing the print image while causing relative movement of at least one of a print head that ejects droplets of the ink and the printing object relative to each other, and the printing control conditions include a speed of the relative movement.
Preferably, the image printing section includes a print head that ejects droplets of the ink, and a relative movement section for causing relative movement of at least one of the print head and the printing object relative to each other, and the printing control conditions include a speed of the relative movement.
Generally, if a time period (drying time) which ink of print dots takes to become dry changes, the penetration rate changes at which the ink penetrates into a printing object before the ink becomes dry. If the penetration rate changes, the size of the print dot also changes. Therefore, when the penetration rate of ink into a printing object has changed, if a time period or a time interval from a printing operation for printing an arbitrary print dot to a printing operation for printing a print dot adjacent thereto is uniformly set to a predetermined value, that is, if the printing speed is uniformly set to a predetermined value, print dots adjacent to each other in the direction of printing (direction of relative movement) can be mixed with each other, thereby degrading the quality of a print image. Inversely, if unnecessarily long drying time is secured, the printing speed is unnecessarily lowered.
According to the preferred embodiment of each aspect of the invention, the print image is printed by moving at least one of the print head for ejecting droplets of ink onto the printing object and the printing object relative to each other, and the printing control conditions thereof include the speed of the relative movement. Therefore, it is possible to set the speed of the relative movement as a printing control condition according to the change in the penetration rate, thereby making it possible to change the printing speed. As a result, it is possible to set a printing speed at which a minimum drying time may be secured for maintaining the quality of the print image. Therefore, even if the penetration rate of ink into the tape (printing object) has changed, the quality of a print image printed by using the ink can be maintained. Further, since the print image can be printed at a suitable printing speed in manner varying with the change in the penetration rate, it is possible to prevent an undesired decrease in the printing speed (increase in the printing time).
Preferably, the step of printing the print image includes the steps of feeding the printing object by a unit distance dependent on a slippage of the printing object in response to each pulse of a predetermined unit feed signal, and carrying out printing on the printing object being fed, and the printing control conditions include the number of pulses of the predetermined unit feed signal generated per unit time period.
Preferably, the image printing section includes a signal generating section that generates a predetermined unit feed signal, a printing object feeding section that feeds the printing object by a unit distance dependent on a slippage of the printing object in response to each pulse of the predetermined unit feed signal, and a printing executing section for carrying out printing of the print image on the printing object being fed, and the printing control conditions include the number of pulses of the predetermined unit feed signal generated per unit time period.
According to these preferred embodiments, the printing object is fed by a unit distance dependent on a slippage of the printing object in response to each pulse of a predetermined unit feed signal, and printing is carried out on the printing object being fed. The printing control conditions include the number of pulses of the predetermined unit feed signal generated per unit time period. As described above, the penetration rate of ink changes with the drying time of ink, and the change in the penetration rate changes the size of each print dot. Therefore, when the penetration rate of ink into a printing object has changed, if the printing speed is uniformly set to a predetermined value, print dots adjacent to each other in the direction of printing (direction of feed) can be mixed with each other, thereby degrading the quality of a print image. Inversely, if an unnecessarily long drying time is secured, the printing speed is unnecessarily lowered. To eliminate these inconveniences, it is required to change the printing speed according to the change in the penetration rate.
Generally, slippage of a printing object depends on the printing object. When the printing object is fed in response to each pulse of a unit feed signal by a unit distance dependent on the slippage of the printing object, if it is desired to feed the object at a predetermined printing speed, it is required to output a corresponding number of pulses of the unit feed signal adapted to the slippage of the printing object. Inversely, it is possible to change the printing speed by changing the number of pulses of the unit feed signal. Therefore, in the preferred embodiment of each aspect of the invention, the printing control conditions include the number of pulses of the predetermined unit feed signal, so that it is possible to set the number of pulses of the unit feed signal according to the change in the penetration rate of ink as one of the printing control conditions to thereby change the printing speed. This makes it possible to carry out printing at the printing speed responsive to the change in the penetration rate. Therefore, even if the penetration rate of ink into the tape (printing object) has changed, the minimum drying time required for maintaining the quality of a print image can be secured, thereby maintaining the quality of the print image printed by using the ink can be maintained, and it is also possible to prevent an undesired decrease in the printing speed (increase in the printing time).
Preferably, the printing control conditions include a gradation value of each pixel of the print image.
According to this preferred embodiment of each aspect of the invention, the printing control conditions include a gradation value of each pixel of the print image. That is, a gradation value which designates a shading or gray level of each pixel of a monochrome image or a color shade of each pixel of a color image can be set as one of the printing control conditions, and hence it is possible to set the gradation value of each pixel in dependence on the change in the penetration rate. This makes it possible to maintain the quality of a print image printed by using ink, even if the penetration rate of the ink into the printing object has changed.
More preferably, the print image is a color image, and the gradation value comprises a plurality of basic color gradation values corresponding to respective basic colors, the at least one kind of ink including inks for printing the plurality of basic colors as respective print colors.
In general, the color shading (color) of each pixel of a color image can be represented by basic gradation values corresponding to a plurality of basic colors into which the color can be decomposed. According to the preferred embodiment of each aspect of the invention, the print image is a color image, and the gradation value comprises a plurality of basic color gradation values corresponding to respective basic colors, the at least one kind of ink including inks for printing the plurality of basic colors as respective print colors. Therefore, by carrying out printing by using inks having the basic colors as printing colors according to the respective basic color gradation values, the print image as a color image can be printed.
More preferably, the plurality of basic colors include three primary colors.
According to this preferred embodiment of each aspect of the invention, the plurality of basic colors include three primary colors. Therefore, the color shading of each pixel of the color image can be represented by decomposing the color of each pixel into the basic color (primary color) gradation values. Further, in this case, the at least one kind of ink includes inks for printing the three primary colors as printing colors. Therefore, by using these inks according to the respective basic color gradation values, it is possible to print the print image as a color image. It should be noted that as the three primary colors, there are normally used C (cyan), M (magenta), and Y (yellow), and various colors are represented by the subtractive color mixing method.
Further preferably, the plurality of basic colors further include a basic color corresponding to a mixed color of the three primary colors.
According to this preferred embodiment of each aspect of the invention, the plurality of basic colors include a basic color corresponding to a mixed color of the three primary colors. Therefore, the inks used further include an ink of the basic color corresponding to the mixed color of the three primary colors. For instance, although mixture of the three primary colors of C (cyan), M (magenta), and Y (yellow) provides K (black), a more beautiful black can be obtained by using an ink of K (black) than by actually mixing the primary colors, and hence the preferred embodiment of each aspect of the invention makes it possible to print a beautiful print image by using the four (basic) colors.
Preferably, the method further includes the step of designating a printing mode out of at least two of an image quality-preference mode for printing the print image with a higher image quality, a printing speed-preference mode for printing the print image with a faster printing speed, and an optimal print mode for printing the print image with a moderate image quality and a moderate printing speed, and the step of setting printing control conditions includes setting the printing control conditions according to the designated printing mode, in dependence on results of detection of the factors causing the change in the penetration rate.
Preferably, the image printing device further includes a printing mode-designating section for designating a printing mode out of at least two of an image quality-preference mode for printing the print image with a higher image quality, a printing speed-preference mode for printing the print image with a faster printing speed, and an optimal print mode for printing the print image with a moderate image quality and a moderate printing speed, and the printing control condition-setting section sets the printing control conditions according to the designated printing mode, in dependence on results of detection of the factors causing the change in the penetration rate.
Depending on penetration rate of ink into the printing object, if further drying of ink is awaited after completion of printing of desired print dots at the cost of a printing speed and then adjacent print dots are printed, it is sometimes possible to improve the quality of a printed image, e.g. by increasing the print density. Inversely, there can be a case where a print image is desired to be printed as fast as possible on condition that the minimum quality of the print image is maintained. In the preferred embodiment of each aspect of the invention, a printing mode is designated out of at least two of an image quality-preference mode for printing the print image with a higher image quality, a printing speed-preference mode for printing the print image with a faster printing speed, and an optimal print mode for printing the print image with a moderate image quality and a moderate printing speed, and the printing control conditions are set according to the designated printing mode, in dependence on results of detection of the factors causing the change in the penetration rate. Therefore, the image quality and the printing speed can be enhanced to respective allowable extents dependent on the user""s selection of the mode, which makes it easy to print a print image of desired quality at a desired speed, thereby increasing the operability and capability of the apparatus in image printing. It should be noted that the optimum printing mode is a mode in which printing control conditions are set which make moderate both the image quality and the printing speed, which may be default settings or the most frequently used ones of the printing control conditions. Further, the image quality-preference mode includes a mode in which the print image having the highest quality is set within an allowable range, and similarly, the printing speed-preference mode includes a mode in which the highest printing speed is set within an allowable range which permits the minimum quality of print images to be maintained.
Preferably, the factors causing the change in the penetration rate include a type of the printing object.
As described above, even if each ink droplet is ejected to the center of a corresponding print dot, the size and density of each print dot depend on the degree of penetration (penetration rate) of ink into the printing object, so that a printed image is sometimes prevented from having a desired image quality, even if printing control conditions, such as a print density and the like, are set to predetermined setting values. In the preferred embodiment of each aspect of the invention, the factors causing the change in the penetration rate include a type of the printing object. That is, the type of the printing object is detected as one of the factors causing the change in the penetration rate, and hence it is possible to discriminate between different penetration rates dependent on the type of the printing object. When the penetration rate has changed from a value initially set or a value set the last time, the change in the penetration rate can be detected. This make sit possible to set printing control conditions, such as a print density and the like, according to the change in the penetration rate, whereby the quality of a print image printed by using ink can be maintained, even if the penetration rate has changed.
Preferably, the type of the printing object includes a material of the printing object.
Generally, if printing objects are different in material, the penetration rate of ink is different between the printing objects, even if the ink itself is identical. In the preferred embodiment of each aspect of the invention, since the type of the printing object includes a material of the printing object, and the change in the penetration rate due to a difference in the material of the printing object can be detected, printing control conditions, such as a print density and the like, can be set according to the change in the penetration rate.
Preferably, the type of the printing object includes a size of the printing object.
In general, if printing objects are different in size from each other, a print unit to be printed on one printing object, such as one dot line of print dots and the like, takes a different printing time from a print unit to be printed on another printing object, so that the drying time which ejected ink takes to become dry can vary with the printing object, that is, depending on the difference in time elapsed between printing of a print unit (line of print dots) and printing of the following print unit(line of print dots) on each printing object. This sometimes changes the penetration rate before the ink becomes dry. This also can change the print density and the printing speed which enable a print image to be printed with the quality thereof being maintained. In the preferred embodiment of each aspect of the invention, the type of the printing object includes a size of the printing object. Hence, it is possible to detect the change in the penetration rate at which ink penetrates into the printing object before the ink becomes dry. This makes it possible to set printing control conditions, such as a print density, according to the change in the penetration rate.
Preferably, the factors causing the change in the penetration rate include at least one of ambient temperature and ambient humidity.
In general, if the ambient temperature has changed, the drying time of ink also changes, which can change the penetration rate at which the ink penetrates into the tape before the ink becomes dry. In the preferred embodiment of each aspect of the invention, the factors causing the change in the penetration rate include at least one of ambient temperature and ambient humidity. That is, at least one of the ambient temperature and the ambient humidity is detected, so that it is possible to determine the difference in the penetration rate of ink into the printing object, which is caused by the difference in the detected ambient temperature and/or the ambient humidity, and thereby detect the change in the penetration rate. This makes it possible to set printing control conditions, such as a print density according to the change in the penetration rate. As a result, even if the penetration rate of ink into the printing object has changed, the quality of a print image printed by using the ink can be maintained.
Preferably, the factors causing the change in the penetration rate include the number of print dots existing in a predetermined unit printing area on which printing has already been carried out.
If the number of print dots existing in a predetermined unit print area varies, the drying time of ink also varies even if the ink is identical, which can change the penetration rate at which the ink penetrates into the printing object before the ink becomes dry. In the preferred embodiment of each aspect of the invention, the factors causing the change in the penetration rate include the number of dots existing in a predetermined unit printing area on which printing has already been carried out (cumulative number of print dots), whereby the change in the penetration rate of ink in use can be detected. This makes it possible to set printing control conditions, such as a print density, according to the change in the penetration rate. As a result, even if the penetration rate of ink into the printing object has changed, the quality of a print image printed by using the ink can be maintained.
Preferably, the factors causing the change in the penetration rate include a condition of whether a transparent laminating material is laminated onto the printing object, and the method includes the steps of determining whether the transparent laminating material is to be laminated onto the printing object, and laminating the transparent laminating material onto the printing object such that the transparent laminating material covers the print image printed on the printing object, when it is determined that the transparent laminating material is to be laminated onto the printing object.
Preferably, the factors causing the change in the penetration rate include a condition of whether a transparent laminating material is laminated onto the printing object, and the image printing device includes a lamination-determining section for determining whether the transparent laminating material is to be laminated onto the printing object, and a laminating section for laminating the transparent laminating material onto the printing object such that the transparent laminating material covers the print image printed on the printing object, when it is determined that the transparent laminating material is to be laminated onto the printing object.
Generally, when a printed image is laminated with a laminating material, the image is protected by the lamination. On the other hand, since ink is made far more difficult to become dry than before the lamination, the drying time of the ink changes, whereby the penetration rate at which the ink penetrates into the printing object before the ink becomes dry can be changed. This also can change an appropriate print density and an appropriate printing speed which permits a print image to be printed while preserving the quality thereof. Further, when an image printed by using the ink is laminated before the ink becomes dry, the ink can be exuded and adversely affect the following print image by changing the penetration rate and adhering to a laminating device or mechanism, so that it is required to laminate the printed image when the ink is sufficiently dry after being ejected for printing.
In the preferred embodiment of each aspect of the invention, the factors causing the change in penetration rate include a condition of whether or not a printing object is to be laminated with a transparent laminating material. When it is detected that the lamination is to be executed, the printing object is laminated with a transparent laminating material such that the laminating material covers an image printed on the printing object. That is, it is possible to determine the difference in the penetration rate of ink into the printing object, which depends on whether or not the lamination is executed, and thereby detect the change in the penetration rate. Accordingly,i tis possible to set printing control conditions, such as a print density and a printing speed. As a result, even when the penetration rate of ink into the printing object has changed, the quality of a print image printed by using the ink can be maintained. It should be noted that when the execution or no-execution of the lamination corresponds to a type of the printing object, detection of whether or not the lamination is to be carried out may be effected as part of detection of the type of the printing object. Alternatively, if the lamination can be effected on an arbitrary printing object, the apparatus may be configured such that the user can set whether or not the lamination is executed and results of the settings are detected.
Preferably, the printing object is a tape.
In this preferred embodiment of each aspect of the invention, since the printing object is a tape, the invention can be applied to a tape printing apparatus.
Preferably, the print image is printed by an ink jet printing method.
In this preferred embodiment of each aspect of the invention, since the print image is printed by an ink jet printing method, the invention can be applied to a printing apparatus based on the ink jet printing method.